Field of the Invention
The present invention relates to a power (electric power) transmission device capable of supplying power generated by a DC power supply such as a photovoltaic power generation device to a commercial power supply for a dwelling house or the like so as to allow the power to be consumed in the house or the like, for example.
Description of Related Art
Conventionally, there has been proposed a device that transmits a power from a DC power supply such as a photovoltaic power generation device to a commercial power system connected to an AC power supply, with the phase matched with voltage of the AC power supply (Patent Document 1). This device converts a magnitude of voltage of the DC power supply into a magnitude of voltage necessary for power transmission to the commercial power system and controls an AC switch configured by a transistor bridge in synchronization with voltage of the AC power supply, to cause AC current (electric current) to reversely flow with the phase matched with the AC power supply.
In such a device, for example, as shown in FIG. 5, a DC-DC converter 51 with an isolation transformer is used for converting a voltage inputted from a DC power supply 50. The DC-DC converter 51 is switched, by a switching element 52 such as a transistor, between a closed state in which a current from the DC power supply 50 flows to a primary side of the isolation transformer, and an open state in which the energy accumulated in the closed state is released and the current flows to a secondary side of the isolation transformer.